Squid Dissection

Purpose

Materials

Thawed squidCleaned and sanitized scissors

Method

Part 1: External anatomy

1. Place squid on paper towel instead of a dissecting tray - there is lots of liquid, and pins are not needed.

2. Locate the head, tentacles, and two eyes. The head and tentacles are the ventral region of the animal, while the two fins are the dorsal surface. There are 4 pairs of arms and two elongated tentacles.

3. The body is covered by the mantle that forms a sheath around the visceral mass which contains many of the internal organs. Locate the siphon on the posterior surface where the head and mantle meet. The siphon is used to expel water from over the gills and as a means of jet propulsion.

4. The squid does not have a skeleton, but rather a chitinous quill. You can feel it through the mantle on top of the anterior side.

5. At the centre of the head, in the middle of where the legs and tentacles are attatched, locate the mouth and two beaks.

Part 2: Internal anatomy

1. Place the squid siphon side up on the paper towel. Make a lengthwise cut along the mantle from the siphon up to the tip of the fins. Open the mantle carefully and locate the gills, siphon retractor muscle, eggs or spermatic sac, stomach, valce, inc sac, and digestive glands.

2. On the anterior surface, find where the water would enter the mantle. Tace its path over the gills and exit through the siphon. You should see brachial hearts at the base of the gills. Squids, unlike most molluscs, have a closed circulatory system. Locate the anus near the inc sac. Move the head to one side and remove the quill.

3. On the posterior surface, make a careful cut from the mouth back between the eyes to the siphon. Be careful not to damage any of the organs in the head. Locate the brain. Remove and cut open one of the eyes. Despite being an inveribrate, squids have a lens and a retina just like the vertibrates.

4. Remove the buccal mass and pull out both halves of the beak

5. Dispose of all internal organs. Keep the mantle, legs, and tentacles for calamari.

Analysis

1. Q: How are arms and tentacles similar and different? A: Similarities - Have grippers to grab prey and move along the ground or ocean floor. Are attatched at the front of the head at the ventral surface of the squid. Are edible. Differences - Tenticles are much longer than the arms, and end with a foot-looking bulge at the end. Suction cups are only located at the end of the tentacles, while they are seen all along the arms. There are 8 arms and only 2 tentacles.

2. Q: How are cephalopods different and similar to bivalves? A: Similarities - Belong to the Mollusca phylum. Have somesort of a chitinous shell. Breathe using gills. Differences - Cephalopods are motile, while bivalves are sesile. Cephalopods hunt for their food, while bivalves feed by filtering nutrients out of water. The shell in a squid is in the form of its quill inside the body, while a bivalves shell surrounds its body, protecting the vulnerable organs within. Cephalopods have very advanced eyes like those of vertebrates, while bivalves have no apparent sensory organs at all.

3. Q: Was your squid a boy or a girl? How did you determine this? A: Our squid was a male. Female squids have a yellow, jelly-like substance underneath the mantle; these are eggs. The males have a milky substance within their mantle; this is sperm.

4. Q: Trace the path of food through your squid. A: After capturing its prey, the food enters the squid through it's mouth. The food travels through the squids digestive glands to its stomach, where the food is digested. Nutrients are taken into the bloodstream and absorbed by muscles throughout the body, and any wastes travel out of the anus located above the head of the squid.

5. Q: Why are the brachial hearts so close to the gills? A: The short distance means oxygen has to travel less distance, therefore making it to the heart faster. This allows for the more effective and efficient distribution of oxygen throughout the body, as well as the removal of carbon dioxide.